It is known from Swedish Patent Application No. 9100372-3 to metallize or plate individually plastic CD-discs and like articles for instance, of low melting point while using a metal smelt, for instance an aluminium smelt of relatively high temperature which is briefly held very close to the article to be coated. The method enables articles to be quickly coated or plated while minimizing the deposit of metal at wrong positions.
One of the problems that occur when using an aluminium smelt as the vapourization source resides in maintaining the actual crucible intact. The aluminium smelt in a vapourization source is heated to much higher temperatures (for instance temperatures above 1,200.degree. C.) than those applied in casting operations and similar operations (for instance 800.degree. C.). This means that the actual aluminium smelt will be much more aggressive and behave as a corrosive acid. Since, among other things, it is desired when carrying out the aforesaid method to achieve long periods of use, on the order of one-hundred hours or more, before it is necessary to replace the smelt and crucible, the demands placed on the crucible are greater than the crucible is able to manage when applying hitherto known techniques.
One troublesome circumstance is that the crucible is used in vacuo, i.e. any small aluminium leakages that occur are not sealed automatically by oxidation of the aluminium on the outer surface of the crucible. Crucibles which are self-sealing in ambient atmospheric conditions will thus continue to sweat or to leak in vacuum conditions, which is unacceptable.
In other words, there is a need for a crucible that is intended for molten aluminium and its alloys or compounds to manage high temperatures and to remain impervious even in vacuum conditions.